Tree roots showing above ground are never good news. They make it difficult to mow your lawn, risk the blades of mowers damaging the tree roots impacting the health of the tree, possibly even killing it.
Moreover, if you have kids running around the garden, you’ll need to know how to fix exposed tree roots to eliminate the trip hazard.
It’s rarely a good idea to start pruning tree roots. They’re super important for the health of the tree, and depending on the diameter of the exposed tree roots, they could also be stabilizing it, anchoring the tree to the ground, preventing it from tumbling.
Taking away more than 20% of a trees root structure can destabilize it.
The only time it’s recommended to prune the roots of trees is when it is absolutely necessary. Like, when the tree is close to a building and the exposed tree roots risk causing structural problems. In a situation like that, you may have no choice but to prune the roots.
Even in those cases, it’s preferable to use the services of a qualified tree surgeon who can identify the most appropriate roots to prune back with minimal damage to the tree.
Depending how close the tree is, it’s age, and the diameter of the exposed roots, it may be the case that the tree needs to be removed.
Understanding Tree Roots
The main tree roots are often at least two to three feet deep into ground soil. Feeder roots, which are often referred to as the ‘suckers’ are found 12 to 18 inches below the soil surface.
When tree roots become exposed, the majority of the time it will be feeder roots rather than any of the major roots.
When they appear above-ground, the cause is the soil because the roots of trees do not change direction in the way some plants do when they’re struggling to get enough water and air.
When tree roots become exposed, it is because of soil erosion.
What Causes Soil Erosion?
Wind, water and gravity are the three main culprits responsible for soil erosion. The problem is exasperated on the soil surrounding trees on hillsides because of the force of water streaming downhill and the increased winds.
When dealing with exposed tree roots, it’s not enough to learn how to fix exposed tree roots because despite pruning being the simplest option, it is not addressing the cause.
The leading cause of tree roots becoming visible above-ground is running water. The more running water effects the soil, the faster the soil will erode.
Additionally, any gardening activity around a tree will disturb the ground, which can cause it to dry out faster, further increasing the speed of erosion.
Another factor that needs to be considered when gardening near trees is tilling. If you’re working on a garden project that needs you to disturb the ground soil, you need to know the boundaries of the tree to prevent damaging the roots, or disturbing the ground soil that’s responsible for the tree’s roots.
In most cases, best practice is to create a boundary extending a few inches beyond the canopy of the tree. The area under the canopy is where you’re best to keep tilling equipment away from and treat that area with a ground covering, such as mulch or different chippings to create a sort of mini-garden under the tree canopy.
The thing to remember about the roots of trees is they will expand several feet in any direction from the trunk.
The benefit of using hard aggregates and other materials for a canopy garden under a tree is you won’t need to take gardening equipment near that area, which results in a more consistent ground structure, helping to maintain the tree’s health.
Given that the cause of exposed tree roots is soil erosion, it’s logical to think you can top the soil up to cover up the roots. Don’t do that.
Dumping several inches of topsoil over above-ground tree roots can result in root shock damaging the health of the tree.
It can also smother the roots, starving them of the oxygen and water they need to keep the tree healthy. Either way, dumping inches upon inches of extra topsoil is unlikely to end well.
How to Deal with Exposed Tree Roots
1 – Build a Mulch Bed Under the Tree’s Canopy
Mulching is considered the most effective way to cover exposed tree roots. Ideally, only around 2 to 3 inches of organic mulch is needed.
This is the best approach for gardens with lawns where the tree roots are only just above-ground, but enough that you can’t mow the lawn without damaging the exposed roots of the tree.
Mulch bed materials to replace turf with include:
- Wood chips
- Composted leaves (the larger the better)
- Bark nuggets
- Pine needles (sometimes referred to as Pine Straw)
Pine needles are probably the cheapest option and it breaks down much slower than bark. It’s also highly porous, so even adding inches of it as a mulch bed still allows plenty of water to filter through to the tree roots.
The downside is that pine needles are the most light-weight and given a lot of exposed tree roots are on sloping grounds, you’ll need to find ways to hold it in place, preventing it from blowing away.
If you need to lay a mulch bed over exposed tree roots in a windy spot, heavier aggregates such as rocks and pebbles are better choices as they still allow water and air to pass through.
These are also the materials to use if you want a once-and-done mulch bed as these are inorganic so unlike pine needles/straw, they won’t decompose into the soil needing mulch top ups to be done every year.
Something to note is that mulch can contribute to root rot when installed against the trunk of the tree. It’s best to leave a 12-inch gap from the tree trunk when laying mulch to prevent excess moisture building up against the bark of the tree.
2 – Overplant the Area with Ground Covering Plants
Planting around and under trees is tricky because there’s impaired sunlight and the tree roots are going to absorb the majority of the water so the only suitable types of plants will be drought tolerant and either grow sufficiently with little sunlight or be able to grow in the shade.
The only way to grow a sort of mini-garden under a tree is to limit your plant selection to small dwarf-type plants. The type that require minimal soil disturbance.
When planting around trees, be careful not to plant anything too close to feeder roots. Remember, the feeder roots are the ones closest to the soil surface, usually 12 to 18 inches.
Feeder roots are typically up to 2-inches in diameter and it’s these roots that absorb nutrients, passing them down to the deeper tree roots that extend to depths of two to three feet and deeper below ground.
When digging a hole to plant any type of plant, be careful not to split any of the feeder roots. Use a trowel rather than a spade so that you can inspect the surface to notice any roots and when you do spot them, move the hole for your plant 2 to 3 inches away from feeder roots so as to avoid the plant competing for nutrients.
The tree roots will always absorb more than miniature plants, making it difficult for new plants to establish healthy root systems.
The same 12-inch rule that should be applied to mulching around trees also applies to planting around the base of a tree. Anything that holds moisture should be at least 12-inches away from the tree trunk.
In the early days after planting, you will likely need to over water new plants as they will be competing with more established tree roots for nutrients.
If you do decide to plant under your tree, an annual top up of organic mulch that’s layered to at least 3-inches will be needed to help enrich the soil, which in turn helps plants establish stronger rooting systems.
In the first year after planting, avoid fertilizers as those only help with top growth. For longevity, you want new plants to focus their energy towards root growth as they are going to need strong root systems to help them compete with more established tree roots for soil nutrients.
3 – Pruning Exposed Tree Roots
As previously mentioned, pruning exposed tree roots should be a last resort and there are situations when it can’t be avoided, such as when the roots are damaging a building’s structural integrity, or perhaps causing a driveway to buckle.
If you need to kill some tree roots to save a driveway, bricked or paved concrete pathway, it’s preferable to know how to kill tree roots without killing the tree.
Most tree species typically only have 4 to 7 major roots. Those are responsible for as much as 25% of the root system. The rest are smaller feeder-roots and that’s what you want to be trimming back.
The roots that are less risky to pruning are those less than 2-inches in diameter and the safest to cut are those farthest away (at least 1-foot away) from the tree trunk.
If you need to learn how to fix exposed tree roots that risk damaging surrounding property, pruning and killing the tree roots is likely necessary.
In gardens where the exposed tree roots aren’t causing any serious risk other than a trip hazard and a nuisance to mow around, a ground covering (either with drought tolerant and shade loving plants) or a mulch bed will be sufficient to cover-up above-ground tree roots.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.
Tuesday 9th of August 2022
I just found your web site and find it very informative and ideas that are easy to digest. It covers a wide variety of issues a homeowner who gardens may encounter. Heading out to mulch my lilacs vs. add topsoil! Thanks for the info!